Packet Communication Device Which Selects an Appropriate Operation Mode

1. A packet communication device comprising: a connection interface unit for connecting to an external device; an external device discrimination unit which receives a notice of a connection to the external device from the connection interface unit, transmits a polling packet to the connected external device and determines whether the connected external device is an upstream device or a downstream device on the basis of a response packet to the polling packet; and an operation mode switching unit which switches to an upstream mode if the connected external device is the upstream device and switches to a downstream mode if the connected external device is the downstream device, the operation mode switching unit performing only any one of the switching to the upstream mode and the switching to the downstream mode on the basis of the determination by the external device discrimination unit, the switching to the upstream mode and the switching to the downstream mode being done independently of each other.

2. The packet communication device according to claim 1 , wherein the operation mode is related to operations of a data transfer unit which transfers a received packet and a control signal processing unit which processes a control signal for the packet communication device.

3. The packet communication device according to claim 1 , wherein transmission of the polling packet to only an upstream or a downstream of the connection bus connected to the external device is permitted by standard specifications.

4. The packet communication device according to claim 3 , wherein the standard specifications are a PCI express.

5. The packet communication device according to claim 1 , wherein the bus connection is a PCI express.

6. The packet communication device according to claim 5 , wherein selection of the operation mode is selection of a mode on an upstream PCI-PCI bridge and a downstream PCI-PCI bridge in a PCI express bridge.

7. A packet communication method comprising: recognizing a connection to an external device and issuing a polling packet to the connected external device, by a packet communication device; determining whether the connected external device is an upstream device or a downstream device on the basis of a response to the polling packet; switching to an upstream mode if the connected external device is the upstream device, and to a downstream mode if the connected external device is the downstream device, only any one of the switching to the upstream mode and the switching to the downstream mode being performed on the basis of the determined result, the switching to the upstream mode and the switching to the downstream mode being done independently of each other; and completing a device-setting according to the switched mode before the entire packet communication device or a part of the packet communication device which is influenced by the switching starts a service to the external device, by the packet communication device.

8. The packet communication method according to claim 7 , wherein the operation mode is related to a data transfer method of transferring a received packet and a control signal processing method of processing a control signal.

9. The packet communication method according to claim 7 , wherein transmission of the polling packet to only an upstream or a downstream of the connection bus connected to the external device is permitted by standard specifications.

10. The packet communication method according to claim 9 , wherein the standard specifications are a PCI express.

11. The packet communication method according to claim 7 , wherein the bus connection is a PCI express.

12. The packet communication method according to claim 11 , wherein selection of the operation mode is selection of a mode on an upstream PCI-PCI bridge and a downstream PCI-PCI bridge in a PCI express bridge.

13. A non-transitory computer-readable storage medium storing a packet communication program which causes a computer included in a packet communication device to execute a process of recognizing an external device connected to the packet communication device and issuing a polling packet to the connected external device, a process of determining whether the connected external device is an upstream device or a downstream device on the basis of a response to the polling packet, a process of switching to an upstream mode of the connected external device is the upstream device, and to a downstream mode if the connected device is the downstream device, only any one of the switching to the upstream mode and the switching to the downstream mode being performed on the basis of the determined result in the process of determining, the switching to the upstream mode and the switching to the downstream mode being done independently of each other, and a process of completing a device-setting according to the switched mode before the entire packet communication device or a part of the packet communication device which is influenced by the switching, starts a service to the external device.

14. The non-transitory computer-readable storage medium according to claim 13 , wherein the operation mode is related to operations of a data process of transferring a received packet and a control signal process of processing a control signal to a device.

15. The non-transitory computer-readable storage medium according to claim 13 , wherein transmission of the polling packet to only an upstream or a downstream of the connection bus connected to the external device is permitted by standard specifications.

16. The non-transitory computer-readable storage medium according to claim 15 , wherein the standard specifications are a PCI express.

17. The non-transitory computer-readable storage medium according to claim 13 , wherein the bus connection is a PCI express.

18. The non-transitory computer-readable storage medium according to claim 17 , wherein selection of the operation mode is selection of a mode on an upstream PCI-PCI bridge and a downstream PCI-PCI bridge included in a PCI express bridge.